1. Field of the Application
This application is generally directed to wellbore drilling systems and methods, and particularly to valves used in communication of a measurement while drilling system.
2. Description of the Related Art
Valves are used in the field of communication of a measurement while drilling system. In a rotary valve (which can also be referred to in various contexts as a circular valve, rotational valve, reciprocating valve, or oscillatory valve), when the rotor blades align with the stator orifices, the valve is in a maximally closed position, and presents what is referred to as “the minimum flow area” to that portion of the mud stream that passes through the valve, and that results in the largest pressure drop across the valve. In Goodsman (U.S. Pat. No. 4,914,637), Moriarty (U.S. Pat. No. 6,219,301), and Turner (U.S. Pat. No. 6,714,138), this minimum flow area is near the outer diameter (OD) of the rotor blades (when the rotor OD is less than the stator orifice maximum diameter) or is provided by some other pathway, as further disclosed by Moriarty, such as a hole in the rotor blade itself or clearance notches in the stator body. In Malone (U.S. Pat. Nos. 5,375,098 and 5,237,540), the minimum flow area is provided by a large mechanical clearance (gap setting) between the rotor and stator faces. Other examples of valve technology are disclosed by: U.S. Pat. No. 5,249,161 to Jones et al.; U.S. Pat. No. 5,586,083 to Chin et al.; U.S. Pat. No. 6,105,690 to Biglin, Jr. et al.; U.S. Pat. No. 6,970,398 to Lavrut et al.; U.S. Pat. No. 6,975,244 to Hahn et al.; and U.S. Pat. No. 7,808,859 to Hahn et al.